Different morphometric parameters have been applied to the study of the morphological differences between a group of normal placentae and a group of placentae collected from Class A diabetic women. It has shown that although fetal weights were significantly higher in the infants of the diabetic mothers, placental weights showed only a tendency to be heavier than the gestationally matched controls, though the difference was not statistically significant. However, the placentae of the Class A diabetic mothers were shown to differ from the control group by having significantly more parenchymal and villous tissues and a higher cellular content. There were also more surface areas of exchange between mother and fetus, in terms of peripheral and villous capillary surface areas and intervillous space volume. On a functional basis, these morphological changes suggest that, in diabetes mellitus Class A, the placenta can efficiently support the growth of a large fetus, and the perinatal associated with this condition is not likely to be related to decreased or insufficient function of the placenta.